Skyline/Goldwing Sbach 60" Build Day #3

Today I essentially completed the Sbach 60" (it's called a 70 for some reason, maybe the nitro engin size?). But like a building that's not done until the capstone is set in place, my Sbach isn't really done until the spinner is put on, and I still have some of the decals to put on.

 

First of all, today's minor annoyance. The wing securing screws are plastic, and the right wing one was stripped because the nut embedded in the wing was obstructed. When the packer put the screw in it stripped, so I had to replace it. It was M5, so I picked up a couple M5 cap screws at Home Depot. in the pic above, the left one is original, the middle the M5 cap screw, and the last the hybrid I made. I cut the plastic screw with a small tab left, which. I shaped it to fit in the hex top of the cap screw, applied some superglue and joined them. The cap screw top is a bit small to screw into the wing, so the thumb accessible top is nice. It's not supposed to be gorilla-tight, so doesn't need to tolerate a whole lot of torque. I was able to clear the obstruction with a cap screw. Works fine!

 

Major project for today is the cowl. I created a paper mock up and had marked the cowl bolt holes where I wanted them, midline and 10mm below the top and bottom edge. drilled the pilot holes.

 

The end of the fuse where the bolts will go before drilling.

 

Pilot holes drilled. Stepped up to 3 mm.

I used a trick I learned from building my Eflite Stearman (still have another one of those NIB) to transfer the holes in the fuse to the holes to the cowl. I tape a piece of paper or card to the side of the fuse and poke a hole through the paper into the drilled fuse hole. Place and center the cowl and drill a pilot hole into the cowl using the paper template.

 

I thought I had pics of how I set up the nuts inside the fuse. I didn't want to use servo wood screws which weaken over time, so I took M3 flat nuts and washers and fixed them into place. I inserted the M3 bolt just deep enough for the washer and nut to secure, with a small tip beyond. I used a small piece of hard wood to wedge between a flat spot on the nut and the firewall to hold it against torque and super glued it in place. I then set each one in epoxy. Once it dried I popped the bolt through the epoxy. I could of used those self wedging nuts with teeth, but I didn't have any and could find M3 sized ones at Home Depot. Once I had set the cowl in place, I used rubber grommets from my heli stock and used them to protect the fiberglass cowl. I had M3 fiber washers but I had changed my mind and used M4 bolts.

 

Cowl in place and all done. The prop plate is about 2mm forward of the front edge of the cowl. Perfect. Came out precisely centered (I set the motor without any offset)..

 

 

Put a couple of the stickers on, will finish those later. Once the spinner is on, I'll put the whole thing together and take some picks.

 

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Skyline/Goldwing Sbach 60" Power Test

This morning I watt tested the electrical power system. I used a 6S 40c 4000mAh battery partially charged to 3.9V, the prop was an APC 17x7 electric.

At max throttle it spiked to 53A when I punched it but ran sustained 46A and produced 1046 watts. I suspect it will run fine on 8S, I have a lot of amp buffer on the 80A ESC. She produced a lot of thrust: I did this in an empty room adjacent to the master bathroom aligned with the bathroom door, where my wife was in the shower, and she said she felt the airflow into the shower stall. The shower rug was blown over. I was about 8-10 feet from both of them.

Right now all of my 4S batteries are damaged, so I am waiting for new ones. When they arrive. I will try two of them in series for 8S 6600 mAh with the wattmeter and see what she does. I am very curious where her CG will lie before adjusting, there is so much mass up front. I don't know if she will fly heavy sluggish with the weight of 6600 mAh. She will maiden on 6S 3300 mAh or 4000mAh. I can also series two 3S batteries for 6600 mAh. I may also move up to a 17x8 prop.

Took the opportunity to set up and program the servos. I won't decide on spoilerons or flaperons until I see how she handles in ground effect and on approach.

Couple of other minor annoyances. Noted the spinner was missing from the kit. I suppose there should be one since it's in the photos on the website. I asked General Hobby to send one but in the meantime ordered another Dubro one. I would like a pointy electric Ultimate spinner, but they are hard to find. Second issue was the plastic finger screw that secures the right wing doesn't fit it's nut snugly so it continues to spin when screwing it in... Will make a Home Depot run this morning to find what I think at M5 screws to replace bothe sides.

 

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Skyline/Goldwing Sbach 342 60" Build Day #2

One long build day today! Got the Honey-Do list done this morning, and set to it!

 

Elevator installed. This is a single servo-U Bar system. The elevator servo is attached to the right elevator which it moves directly. The U-bar transfers the movement to the other elevator to which it's attached. One end of the U is in the right elevator, the other in the left elevator. If the elevators are not equally deflected, a roll force occurs as if they were ailerons. The hard steel I think they intended for the U-bar snapped when I shaped it, too brittle, and the softer steel rod (I think intended for throttle control rod not needed on an electric) torqued too much at full deflection. I ended up adding the left over hard steel rod (see below) as an anti-torque bar and it worked it great!

 

 

Clean install, you can see the silver U-Bar.

 

Elevator servo without extension. The aluminum control arm is standard length, shorter than the supplied fiberglass one. Inadequate throws, I mean, good, but not complete. The geometry is off with the servo end below the elevator carol horn.

 

So I modified the setup by laying the fiberglass arm over the aluminum arm.Perfect geometry.

 

 

Side view. Trimmed the screw ends for a cleaner look. Now get full throw range of motion.

 

 

Zaphod, sleeping on the job... Just can't get good help these days.

 

The aircraft, like many, benefits from an underside tail vent opening to improve ventilation across the motor, ESC and battery. I made that opening, and then created a louvre system to direct the air. I had seen this mod on RC Universe on this model and liked the way it looked. I had no idea how to make it but McGyvered a fairly decent set. First made a box that fit in the opening and created a jig for the louvers, cutting guide slits.

 

I added a scoop for the inside tail end to further direct air out the hole.

 

Super glued in construction then coated with alochol thinned epoxy for strength and sealing. I painted it matte black.

 

The vent opening. When I install the louvers I'll post a pic. I used the needle nose pliers to hold the bar in the grooves.

 

The anti-torque bar. I routered out a slot and dropped the bar in there, superglued it, and later coated it epoxy.

 

The other side.

 

In place before the cote covering. It lies parallel to and just aft of the U-bar, so gluing them together increases the support against torque.

 

After I put white cote over it, and voila, can't see nothin'.

 

Rudder and tail wheel assembly. Rudder control horns are fiberglass one piece. I am not fond of tail wheels that put the stress on the rudder and it's hinges. This design mitigates the stress with a sturdy stabilizing platform with three screws and the collar resting on the plate. I had to find an extra collar, there wasn't one in the kit. Went together nicely. I added a piece of nylon hinge material used for connecting the control surfaces across the bar as it goes up into the rudder to provide more support.

 

Sturdy. You can see the hinge material across the landing gear rod on the rudder.

 

 

I went to a lot of trouble to put the wheel pants on the correct sides. Fail.

 

Fixed. That's better.

 

First time resting in all three landing gear.

 

Takes up the whole breakfast table.

 

Rudder servo with the control arm and wire attachments installed. I haven't used aluminum control horns before, worried about fit. I got Hitec C1 21T spline, and they all had to be tapped (lightly hammered actually) to fit. This one went on by hand, snugly. All of the centered nicely without sub trim.

 

I mark the couplings with red Sharpie to show when I reach 50% of the length so I don't weaken the coupling.

 

 

When setting up the rudder pull-pull system it's important to center everything. I locked the rudder.

 

 

Rudder system is complete.

 

 

Looking aft through the fuselage at the pull-pull system. The wires cross to ensure they exit the fuselage aft in line with the rudder control horns. Snug tension, not stressed. I later secured the elevator servo wire to keep it off the wires.

 

The distance from the motor box to the end of the cowl was 113mm. The motor tfrom base plate to the prop rotor base was 60mm. I had to come up with 53mm. I was annoyed, there is nothing in the instructions on this. I remembered there was a bag with a lot of wood frames in it for the gas tank in a fuel model. I opened it to see if there was some wood I could use, and there was a motor box extension of 50mm! I modified it slightly to make it stronger. I was able to put it together and sort out how I wanted to install it.

 

Measure twice,epoxy once. I measured and centered it (the holes for the center were not centered, glad I ignored them). Epoxied into place and added a M4 bolt and self anchoring nut to ensure it never comes off.

 

Perfect fit! I love it when the engineering math works out!

 

Motor installed. Again, perfect fit! Math, baby! The HobbyWing FunFly 80A HV ESC in place. Plenty of ventilation!

 

I was worried that the deck the reciever was on was kinda thin, and it cracked when I pressed the reciever Velcro into place, so I added a piece of thin plywood as a deck, both repairing the crack and adding strength. Spektrum AR600 DSMX receiver. I like to use short extensions for the aileron servos so I don't mess with the reciever.

 

All the electronics in place. Forward the battery leads are lengthened with segments I salvaged from old batteries. The tap for the BEC is up front and the Exceed RC 6V BEC is Velcroed to the bulkhead (it can be seen in the lower right hand corner, forward in the fuse). The ESC has a spark eliminator circuit built into the wiring harness, but it's too far forward so I can't use it

 

I always take the motor stickers off since the heat will make it fall off anyway, and tape it to the firewall.

 

Long but fruitful build day!

 

UPDATE: Installed the louvers. Look better in real life.

 

 

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Grounded

All of my 4S batteries are toast... recharged and retested them. The wattmeter showed nice numbers until the battery ran beyond a few secs then wild fluctuations in voltage and amps out as the motor waxed and waned. None of them are behaving properly. Threw a 3S on there and it worked fine. I am pretty sure it's not the ESC, But not throwing away the batteries until the new ones test running well. Gnashing of teeth as I ordered new 4S 3300mAh 25-50C Turnigy Nono-tech batteries. Few options...

Guess I need to get the Sbach up and running and maiden her without finishing up getting my flying fingers back fully. thankfully those batteries are fine.

 

UPDATE: screw it... I don't like the cheap ESC in there now, ordered a HobbyWing FunFly 60A with SBEC.

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